I will be shortly relocating to the U.S.A. from th U.K.to live and work permanently.Due to FATCA I have had to liquidate all my investments here and will have to reinvest again once I arrive. I intend to continue with my previous VTSAX/bonds 60/40 allocation but i’m unsure wether I should drip-feed the money in or place the funds with Vanguard in one go when I arrive? I suspect there might be tax implications too. Any advice would be much appreciated.

I will be shortly relocating to the U.S.A. from th U.K.to live and work permanently.Due to FATCA I have had to liquidate all my investments here and will have to reinvest again once I arrive. I intend to continue with my previous VTSAX/bonds 60/40 allocation but i’m unsure wether I should drip-feed the money in or place the funds with Vanguard in one go when I arrive? I suspect there might be tax implications too. Any advice would be much appreciated.

Try to read every relevant post by Ted Swipett here. He went UK to US to UK in his career.

Your UK pension fund money you cannot access (assuming Defined Contribution scheme, not Final Salary -- if you have FS then all you have to do is leave it and keep them informed of changes in address, remember it will be indexed to CPI or RPI up to 5.0% pa, and your spouse gets half pension) until age 55. But I believe under US tax laws you may have to pay tax on it? Or you can go the QROP route (taking your pension offshore) - but there's been some hairy change in the Finance Act for QROPs for *some* countries. I generally formed the opinion that the quality of advice you receive on QROPs is not good (offshore Financial Advisers are not as heavily regulated as UK based ones) and the funds available are high cost. And that won't free you from US tax issues.

The US PFIC rules will kill any investing in funds that are not US domiciled (listed, effectively), I suspect. Thus you have to liquidate-- ETFs too (if they are European ETFs).

Your UK State Pension will still be indexed to RPI + whatever uprating. This is not true if you move to Canada or Australia, where it is frozen at your date of departure, btw . And yes, with inflation protection, even a small amount will be valuable when you retire in 30+ years*.

I would put it in in one go. If that feels too risky, then you should hold fewer equities and more bonds.

If it really would hurt too much then break it into 2 parts - do 50% now and 50% in, say, 6 months time (or even 25% every 3 months). But drip feeding is basically changing your asset allocation, and there is no point to that.

Your major problem though will be tax exempt space? There are low annual limits in the USA for IRAs, 401ks etc. So if potentially you are going to invest in taxable now, and then over time increase your tax deferred/ exempt (401k, IRA etc.) then you have to think about that.

* my father left England in the 1950s, and my mother still gets a widow's pension -- every so often she has to go see a lawyer and swear that she is still alive .

I will be shortly relocating to the U.S.A. from the U.K.to live and work permanently.Due to FATCA I have had to liquidate all my investments here and will have to reinvest again once I arrive. ...

Ah, FATCA. The gift that keeps on giving. Valuethinker has already provided a decent overview. I'll just amplify a bit...

Excluding any UK pensions or SIPPs, presumably? Given what you have done, you might have some UK capital gains taxes to pay, but it is likely that you would have paid far more had you liquidated these investments after becoming a US resident. The US has no annual capital gains tax allowance, and while the federal capital gains tax rates are not dissimilar to UK rates, once you lard US state tax on top the results can be pretty unappealing (for example, around 9% just for California).

Pay extra-special attention to any ISAs. The US simply ignores the ISA wrapper, so if you have appreciated assets in an ISA and you cash them in before arriving in the US you will pay no capital gains tax to any country. Compare with the worst case where you hold US 'PFIC' (Punitive Foreign Income Curse!) investments in an ISA and sell after becoming a US resident -- the US tax bill on this could conceivably reach 100% of your gains (yes, really). Either collapse the ISA entirely, or at minimum hold only US-tax-friendly items in it (direct stocks, direct bonds, cash, but no non-US domiciled funds or ETFs).

As for pensions and SIPPs... the US/UK tax treaty is a bit gray in this area. Most UK pensions are well covered, and so generate no annual US federal tax liability. There is however something of a question over SIPPs in particular. It is reasonably clear that the spirit of the treaty intends to cover them, but the letter of the treaty is less clear and a few professionals err on the side of caution and suggest paying annual tax on these. My advice would be to claim treaty coverage anyway, especially given that the alternative is potentially double-tax on your pensions. I have never heard of the IRS challenging this. Watch out for state taxes in this area; not all states honour the US/UK tax treaty, so you can find yourself on the hook for state taxes on accruals inside a UK pension that you cannot actually touch for decades. Evil. Cross-border pensions are a nightmare. This nightmarish-ness also applies to some extent in the other direction too, by the way, should you invest in a US IRA or 401k and then later return to the UK.

Finally, no particular tax issues with transferring GBP to USD and re-investing in the US using normal US-based facilities. However, the US tax system equates 'foreign' with 'offshore' and 'offshore' with 'illegal', so be on the lookout for the myriad 'information' reporting forms for non-US accounts. For example, FinCEN 114, a complete horror with a 50% balance/year penalty for non-reporting (even though it is purely 'informational' and generates no actual tax liability). In general, be aware that once you enter the US tax system you are in land-mined territory, and that escape is tricky. Virtually nothing works the way you will expect, and the whole tax system is user-hostile and at times appears impenetrable to the uninitiated (and many of the initiated too).